World powers on Friday agreed an ambitious plan to cease hostilities in Syria within a week and dramatically ramp up humanitarian access at talks in Munich aimed at reviving the struggling peace process.

World powers on Friday agreed an ambitious plan to cease hostilities in Syria within a week and dramatically ramp up humanitarian access at talks in Munich aimed at reviving the struggling peace process.

The 17 countries agreed "to implement a nationwide cessation of hostilities to begin in a target of one week's time," said US Secretary of State John Kerry after extended talks co-hosted by Russian Foreign Minister Sergey Lavrov.

The so-called 'International Syria Support Group' also agreed "to accelerate and expand the delivery of humanitarian aid beginning immediately".

"Sustained delivery will begin this week, first to the areas where it is most urgently needed... and then to all the people in need throughout the country, particularly in the besieged and hard to reach areas," said Kerry.

Earlier this month, the Syrian army and allied forces pressed an offensive on the key terrorists' stronghold of Aleppo.

Kerry said talks between opposition factions and the Syrian government would resume as soon as possible, but warned that "what we have here are words on paper -- what we need to see in the next few days are actions on the ground."

For his part, Lavrov called "for direct contacts between the Russian and US military" in Syria and said negotiations on a political transition "have to start as soon as possible, without ultimatums and preconditions".

Kerry said the cessation of hostilities  would apply to all groups apart from "the terrorist organizations" of the so-called 'Islamic State of Iraq and the Levant' (ISIL) and Al-Qaeda affiliate al-Nusra Front takfiri groups.

A UN task force, co-chaired by Russia and the US, will work over the coming week "to develop the modalities for a long-term, comprehensive and durable cessation of violence," Kerry said.